The behavioral manipulation of insect pests for their management, as an alternative to broad-spectrum insecticides, has been investigated for many years.
In addition to the development of resistance against insecticides by the target organism, broad-spectrum insecticides have also negative impacts on natural enemies of the pest insect, on pollinators and on other non-target organisms. Therefore, there is an increased interest in the behavioral manipulation of insect pests for their management as an alternative to broad-spectrum insecticides. Of particular interest are compounds that do not exhibit substantial toxicity or demonstrate some degree of selectivity towards a pest insect and not towards natural enemies, pollinators or the environment. In practice, manipulation may be achieved through the use of stimuli that either enhance or inhibit a particular behavior and ultimately change its expression. Many natural plant defensive chemicals discourage insect herbivory, for example, by deterring feeding and oviposition or by impairing larval growth, rather than by killing insects.
Eugenol is a volatile member of the phenylpropanoid class of compounds from essential oils of many spices, particularly clove (Dewick 2002). Cloves are useful in the home as moth deterrents and the main odorant from cloves, eugenol, has been reported to be perceived as a long-range stimulus by several lepidopterans (Topazzini et al. 1990). One problem with phenylpropanoids such as eugenol and compounds with a cinnamyl framework is that they can produce toxic metabolites after benzylic/allylic oxidation by certain cytochrome P450 enzymes (Dewick 2002).
Several polyphenolic compounds are also known for their toxic/insecticidal effects (Kim and Ahn 2001; Schneider et al. 2000; Khambay et al. 1999; Harborne 1989). Flavonoids isolated from Annona squamosa (Kotkar et al. 2002), Ricinus communis (Upasani 2003) and Calotropis procera (Salunke et al. 2005), are toxic to the pulse beetle. Callosobruchus chinensis and R. communis also caused oviposition deterrent and ovicidal affects in addition to toxicity. Larvicidal activity of lignans, leptostachyol acetate and analogues from the roots of Phryma leptostachya have been reported against three mosquito species (Culex pipiens pallens, Aedes aegypti, and Ocheratatos togoi) (Park et al. 2005).
Compounds derived from aromatic amino acids, such as phenolics, have been reported to be involved in defense of the plant against herbivores and pathogens, as well as in attracting pollinators. For example, phenol derivatives such as guaiacol (1-hydroxy-2-methoxybenzene), 1,2-dimethoxybenzene, 1-ethoxy-2-methoxybenzene, 1-propoxy-2-methoxybenzene, eugenol and isoeugenol, occur in smoke (Guillen and Manzanos 2005; Murugan et al. 2006) and are reported to have insect-repellent and insecticidal activities (Murugan et al. 2006). Furthermore, smoke phenolics taste and smell pleasantly (to humans) (Guillen and Manzanos 2005) and may have antioxidant activity (Bortolomeazzi, et al. 2006). Eugenol (2-methoxy-4-(2-propenyl) phenol), is found in herbs (such as basil, Ocimum suave (Wild.)) and has been reported to have activity against grain beetles as a toxicant and deterrent (Obeng-Ofor and Reichmuth 1997). Other benzene derivatives, such as benzyl alcohol, benzonitrile, phenylethanol, 4-methyl phenol, 4-ethylphenol, 2-methylphenol and benzaldehyde are reported components of human odor that malaria mosquitoes respond to (Hallem et al. 2004; Meijerink et al. 2000).
The gypsy moth, Lymantria dispar, is native to Europe and Asia, where it is a forest pest. It was introduced to Eastern North America in 1868, and it has spread significantly from the original point of introduction (Massachusetts) (Montgomery and Wallner 1988). The moth larvae defoliate mainly deciduous trees, including oak, aspen, ash, willow, apple, alder, birch and poplar. If population density is high, the moth larvae may also attack cottonwood, hemlock, cypress, pine and spruce. This defoliation will weaken healthy trees, but can kill an already weakened tree. During outbreaks, large areas of forest can be defoliated (Montgomery and Wallner 1988). For example, 6 million ha of mixed oak forest were defoliated in 1981 in Pennsylvania during an outbreak. The damage was estimated at $72 million in lost timber and the cost of the spraying program was estimated at $9 million (Montgomery and Wallner 1988).
The gypsy moth begins its life cycle as egg masses, deposited by the flightless female moths on the branches and trunks of host trees. The eggs can be moved around accidentally through the wind and contact with infested trees. This has caused shipment of the moth to other parts of the world (for example, in the early 1990's gypsy moths were accidentally transferred from Asia to British Columbia on ships). The eggs overwinter and hatch in the spring, concurrent with the first buds on the host trees. Larvae then feed on the leaves, causing defoliation. The larvae are very mobile: they spin silken threads that enable them to be carried by the wind or to glide from one branch to another. During mid summer, the larvae reach the pupal stage and 1-2 weeks later the adult moths emerge (Montgomery and Wallner 1988). When females are ready to mate, they emit a sex attractant pheromone. The males follow the plumes of this pheromone upwind, until they reach the female and mate. The females then lay their egg masses in the late summer and the cycle begins anew (Montgomery and Wallner 1988).
The structure of this sex attractant pheromone was determined to be cis (7,8)-epoxy-2-methyloctadecane (disparlure), by isolation of the compound from ˜105 female gypsy moths (Bierl et al. 1970; Bierl et al. 1972). Further research, in which the enantiomers of disparlure were tested against the antennae of male gypsy moths (Grant et al. 1996; Gries et al. 1996; Hansen 1984; Miller et al. 1977) and in field trapping experiments (Miller 1977; Cardé et al. 1977; Plimmer et al. 1977), revealed that (+)-disparlure, cis-(7R,8S)-7,8-epoxy-2-methyloctadecane (+)-1, is the main active component of the sex attractant pheromone of L. dispar. The enantiomer, (−)-1 has been identified as a major component of the pheromone of the nunmoth, a closely related species (Grant et al. 1996; Gries et al. 1996). This enantiomer is not attractive by itself to either species, but prevents upwind flight behavior in the gypsy moth, when presented with (+)-1. The nunmoth also uses (+)-1 as a component in its attractant pheromone, and enantiomer (−)-1 neither attracts nor inhibits the nunmoth (Grant et al. 1996; Gries et al. 1996) This discrimination between blends of enantiomeric and other components has been proposed as one mechanism for species differentiation (Grant et al. 1996; Gries et al. 1996; Gries et al. 2001; Gries et al. 2005).
The structures of gypsy moth sex attractant pheromone, (+)-1, and two behavioral antagonists are as follows.

The moths perceive the pheromone through sensory hairs, sensilla trichodea, on their feather-like antennae (Schneider 1969). Electrophysiological studies with male gypsy moth antennae have revealed that the gypsy moth has innervated sensory hairs that respond only to (+)-1 or only to (−)-1 (Hansen 1984). This means that the moth detects both enantiomers of 1, distinguishes them and integrates the information in the brain. A practical consequence of this enantiomer discrimination is that the number of moths caught in pheromone-baited traps is highest with (+)-1 of high enantiomeric purity (≧98% ee) (Miller 1977). Thus, the pheromone plays a central role in the reproduction of this moth species, and eavesdropping into this pheromone communication has been used in attempts to control the moth.
Gypsy moths are controlled by natural enemies (birds, small mammals, spiders and wasps) as well as some diseases such as nuclear polyhedrosis virus (NPV). For unknown reasons, outbreaks occur on approximately a 10 year cycle, and this is when the moth does the most damage (Montgomery and Wallner 1988). Gypsy moth is monitored successfully with pheromone-baited traps and with selective pesticide applications. Outbreaks in or near urban areas, however, can be a problem because it is difficult to deploy pesticides in these areas. It is also difficult and harmful to other species to deploy insecticides in dense forests. Urban areas and very dense, inaccessible forests are places where non-toxic alternatives to insecticides might be most useful to maintain infestations at or below acceptable levels.
Pheromone-based control methods that have been tested for the gypsy moth fall into three classes: 1) saturation of the air with pheromone to mask the females and cause mating disruption, 2) trapping large numbers of males into strategically placed traps, 3) trapping samples of males in monitoring traps and spraying the appropriate area with an insecticide. (Plimmer et al. 1982; Campion 1984). Of these three methods, the third is widely used to pre-empt outbreaks (Campion (1984). The second approach (mass trapping) has had only limited success because the areas in which mass trapping is necessary, to have a significant impact, are very large. The first approach (mating disruption) carries the risk that large numbers of moths will be attracted to the treated area by the applied pheromone from nearby non-treated zones (Campion (1984). For gypsy moth, mating disruption is complicated by the hydrophobicity of the pheromone, which makes formulation and biodegradation difficult (Campion (1984) and by the high cost of (+)-1.
In nature, host plant odors have been known to synergize with pheromone responses (Bengtsson et al. 2006; Dickens 1989; Dickens et al. 1990; Dickens et al. 1993; Erbilgin and Raffa 2001) and non-host plant odors sometimes antagonize pheromone responses (Landolt and Phillips 1997). Natural (Grant et al. 1996) or synthetic pheromone mimics can also antagonize the response of an insect to its pheromone (Bau et al. (1999); Renou et al. 2002).